RowDefinition not working Properly in VIewBox in Windows8

RowDefinition not working Properly in VIewBox in Windows8

I have created a ViewBox in which I am designing my screen Xaml is like
this->
<Viewbox x:Name="viewbox" Stretch="Fill" >
<Grid>
<Grid.Background>
<ImageBrush ImageSource="/JumblerGame/Images/asd.png" Stretch="Fill"
AlignmentX="Left" AlignmentY="Top"/>
</Grid.Background>
<Grid.RowDefinitions>
<RowDefinition Height="2*"/>
<RowDefinition Height="3*" />
</Grid.RowDefinitions>
<Grid Grid.Row="1" VerticalAlignment="Bottom">
<Grid.RowDefinitions>
<RowDefinition Height="*"/>
<RowDefinition Height="*"/>
<RowDefinition Height="*"/>
</Grid.RowDefinitions>
<Grid Grid.Row="0">
<Image Source="/JumblerGame/Images/qwe.png" Stretch="None" Margin="10"
x:Name="imageplay" Tapped="imageplay_Tapped" />
</Grid>
<Grid Grid.Row="1">
<Image Source="/JumblerGame/Images/bnm.png" Stretch="Uniform" Margin="10"
x:Name="imagesetting"/>
</Grid>
<Grid Grid.Row="2">
<Image Source="/JumblerGame/Images/zxc.png" Stretch="Uniform"
Margin="10,10,10,10" x:Name="imagehelp"/>
<Image Source="/JumblerGame/Images/yu.png" Stretch="Uniform"
VerticalAlignment="Bottom" HorizontalAlignment="Left"
Margin="100,50,100,40" />
<Image Source="/JumblerGame/Images/info.png" Stretch="Uniform"
VerticalAlignment="Bottom" HorizontalAlignment="Left"
Margin="130,50,100,60" />
</Grid>
</Grid>
</Grid>
</Viewbox>
As you can see I have Defined 2 RowDefinitions(Height=2*,Height=3*) for
the Grid and I am working on Row 1 of the Grid but this Row is Taking Full
screen(Space of row 0 too).I want it to be in Row 1 only.
How can I resolve this.???